Recently, chance of getting and leading information of documents and images in a form of electronic information simpler than those in a form of usual printed material on paper is more increased accompanied with increasing in the rapidness of the processing speed of personal computer, spreading of network infrastructure and capacity glowing and cost lowering of data storage.
As the means for leading such the electronic information, liquid crystal displays and CRT are usually used and light emission type displays such as an organic electroluminescent are mainly applied recently. However, it is necessary to observe such the leading means for long time, particularly, when the electronic information is information of documents. Such the action is difficultly considered as a gentle means for the human. As the problems of such the light emission type displays, it has been known that eyes are fatigued by flicker, portability is low, posture for leading is limited and focusing on the still image is necessary and electric consumption is increased accompanied with prolongation of the leading time.
Although memory type reflective displays utilizing outside light which do not consume electric power for sustaining the image have been known as the means for compensating such the defects, such the displays are difficultly considered to have sufficient properties in the present condition by the following reasons.
In the system using a polarizing plate such as a reflective liquid crystal plate, the reflectivity is low as about 40% so that display of white image is insufficiently and majority of the production methods to be used for producing the constituting parts of the display is not always simple is utilized. A polymer dispersion type liquid crystal requires high voltage and the contrast of the obtained image is not insufficient since difference of between the refractive indexes of organic compounds. A polymer network type liquid crystal has problems that high voltage is required and a complex TFT circuit is necessary for improving the memorizing ability. A displaying element using electrophoresis requires high voltage such as 10 V or more and has anxiety about lowering in the durability caused by coagulation of the electrophoresis particles.
As a method of realizing full-color display, an electrochromic method is known, which is drivable at a low voltage of at most 3V. However, when sufficient black and white contrast and further colors are displayed with bright white, 3 layers of different colors need to be layered, resulting in the possibility of high cost due to a complicated element constitution. Further, a full-color electrochromic element via level mixing is known (for example, refer to Patent Document 1). However, in this method, high density black is unrealized due to level mixing, resulting in inadequate black and white contrast. Still further, it is known that a polypyridine compound is used for an electrochromic element (for example, refer to Patent Document 2). However, in this constitution, only 2 colors can be displayed as display colors and black display is specifically unrealized.
As a method to realize black display, an electrodeposition method (hereinafter referred to as an ED method) utilizing dissolution-deposition of a metal or a metallic salt is known (for example, refer to Patent Document 3). Such an ED method is an advantageous method to realize adequate black and white contrast, but in order to display full-color, it is necessary to use color filters of B, G, and R, or Y, M, and C, whereby there has been noted the problem that adequate black and white contrast via this method is unable to be utilized.    Patent Document 1: Unexamined Japanese Patent Application Publication (hereinafter referred to as JP-A) No. 2003-270670    Patent Document 2: Japanese Patent Publication No. 2930860    Patent Document 3: JP-A No. 2003-241227